Nautilus in Midlane and not support:

Nautilus has a lot of CC (Crowd control eg: slow, snare etc...) which is good but the problem is that he has to get in melee range for the CC to do it's job. This is a problem because it means he has to get items to do damage and/or soak up damage.
The only way for him to get enough gold for the items is farming and getting kills/assists.
I find that Nautilus support is not a good role/choice because although he gets assists, he doesn't get enough early gold to get early tank items for allowing easier initiation, with his Dredge Line (Q), a greater chance of survival and getting a kill on the enemy.

I believe Nautilus could be a viable midlaner. This is because there is large kill potential if the jungler ganks at the correct time and Nautilus catches the enemy midlaner with Dredge Line. He gets farm, kills and assists meaning he is able to get all of his items quickly enabling him to reach his full potential as a tanky AP midlaner.